Photolithographic patterning is a well-established technology in the manufacturing processes of various integrated circuits (ICs), including ICs with semiconductor devices and liquid crystal display panels.
In photolithography, a mask is used to selectively expose segments of a resist material to an appropriate energy source or chemical composition to define a pattern in the resist material. The resist material may be converted from a non-acidic or basic resist material to an acidic resist material where exposed. That is, exposure of the basic resist material activates a photo-acid generator (PAG) or a thermal acid generator (TAG) within the resist material to generate acid, making the exposed regions acidic. Either the regions of exposed, i.e., acidic resist material, or the regions of unexposed, i.e., basic resist material, may be removed by a developer in which one of the regions is soluble. In a positive tone development process, the developer is formulated and selected such that the exposed, acidic resist regions are soluble in the developer. A resulting resist feature will, therefore, be formed from the unexposed, basic resist regions after the exposed, acidic resist regions are removed in development. In a negative tone development process, the developer is formulated and selected such that the unexposed, basic resist regions are soluble in the developer. A resulting resist feature will, therefore, be formed from the exposed, acidic resist regions after the unexposed, basic resist regions are removed in development.
Chemical interactions between the acidic, exposed resist regions and the basic, unexposed resist regions may shift an acid-base equilibrium boundary during or after selective exposure of the resist. Therefore, an effective “boundary” between the acidic, exposed resist regions and the basic, unexposed resist regions may not correspond to the intended boundaries defined by the mask used during selective exposure. Thus, use of a mask with a precise, intricate pattern, may not necessarily result in the same precise, intricate pattern being transferred to the resist. In addition to the acid-base equilibrium shift, shadowing effects, topographical and masking complexities, and other limitations of conventional masking, exposure, and development acts, may further result in the formed resist pattern not matching the precision or intricacy of the pattern defined in the mask and may otherwise not meet tolerances as to the precise pattern needed.
Areas of the pattern intended to be void of resist material may be undesirably occupied by resist material due to line merge issues. Similarly, areas of the pattern intended to be occupied by resist material may be undesirably unoccupied by resist material due to line breakage or line collapse issues. For example, when patterning to form a resist feature that is ideally uniform in width and height, such as the resist feature 100 illustrated in FIG. 1, limitations of conventional masking, exposure, and development acts may produce an undesirably disjoined or “broken,” resist feature, such as separated resist features 200 illustrated in FIG. 2. As another example, when patterning to form separated resist features, e.g., separated resist features 200 of FIG. 2, limitations of conventional masking, exposure, and development acts may produce an undesirably joined resist feature, e.g., resist feature 100 of FIG. 1. Thus, line breaks may be formed or, conversely, line merges may be formed where not wanted. As another example, terminating ends of an array of elongate features formed in the resist material may not actually terminate in alignment with one another; some ends may be longer than desired and some ends may be shorter than desired. Such patterning errors may thereafter be transferred to underlying materials during subsequent pattern transfer.
Efforts have been made to account for shadowing effects and other limitations of photolithography processes. Such efforts include optical proximity correction (OPC) methods and phase shift mask (PSM) methods. With OPC, modifications are made to the pattern in the mask to compensate for the patterning errors and enable the desired pattern to be formed in the resist material. Nonetheless, achieving and transferring a precise, intricate pattern in patterning materials remains a challenge with conventional techniques.